The present invention relates generally to methods and apparatus for generating a perspective corrected view of a portion of a wide angle image acquired, for example, by utilizing a fish-eye lens. More particularly, the invention provides methods and apparatus for linking the wide angle image and a perspective-corrected view of a portion of that image.
Imaging systems that utilize fish-eye lenses are known in the art. A fish-eye lens captures an image corresponding to a hemispherical, or a partially hemispherical, field of view. That is, fish-eye lenses allow imaging much-enhanced angular views relative to views obtainable by ordinary camera lenses. An image obtained by a fish-eye lens, however, contains radial distortions that need to be rectified to allow convenient viewing.
Methods and devices for selecting and undistorting a portion of a fish-eye image are also known. Such conventional methods and devices, however, suffer from a number of limitations. For example, although such conventional devices present an undistorted view of a portion of a fish-eye image, they do not allow a viewer to observe simultaneously the relation of the undistorted view to the entire image using a single imaging device. In other words, such conventional devices do not allow a viewer to observe simultaneously an undistorted view of a portion of a fish-eye image, and the remainder of that image, albeit with distortions introduced by the fish-eye lens present.
Moreover, conventional methods for undistorting a portion of a fish-eye image have a number of shortcomings. Such conventional methods can only be utilized for removing distortions from image portions corresponding to a small field of view. For example, these methods break down completely when applied to image portions corresponding to fields of view of tens of degrees, resulting in smeared images. Such limited viewing angles provided by conventional methods diminish considerably the benefits of panoramic observation of a scene.
Accordingly, there is a need for methods and apparatus for acquiring and viewing a fish-eye image that provide canonical undistortion capability, and afford enhanced flexibility for viewing portions of the fish-eye image throughout the full 180-degree field of view while compensating for distortions introduced by the fish-eye lens.
Further, there is a need for methods and apparatus which allow readily selecting a portion of a fish-eye image, generating a perspective-corrected view of the selected portion at a desired magnification without losing the benefits of panoramic aspects of viewing a scene provided by the fish-eye lens.
The present invention provides, in one aspect, a device for generating a perspective corrected view of at least a portion of a wide-angle image. More particularly, the present invention provides a device that utilizes a fish-eye lens coupled to an imager, such as, a CCD or CMOS array, a thermal imaging array or any other suitable optical imaging device, to obtain an image of a scene, for example, an image of a scene corresponding to 180-degree field of view, and displays the acquired image on a primary display. The device further allows selecting a portion of the displayed image for further viewing, at a desired magnification and with distortions introduced by the fish-eye lens substantially removed, on the primary display, or alternatively, on a secondary display.
In another aspect, a device of the invention includes an image-capturing device that generates an image, for example, in the form of a two-dimensional digital map of luminance, of a field of view. The image-capturing device can include a fish-eye lens that collects optical photons emanating from the field of view, and an imager that converts the collected optical photons to electrical signals representing an image of the field of view. This image is herein referred to for brevity as xe2x80x9cfish-eye imagexe2x80x9d. The term xe2x80x9cfish-eye imagexe2x80x9d, as used herein, refers to a hemispherical, partially hemispherical, or more broadly, to a wide-angle image of a field of view. The device of the invention can further include a processor that communicates with the image-capturing device to access the acquired image for processing, such as, removal of distortions introduced by the fish-eye lens.
In a related aspect, the processor includes a first display module that displays the fish-eye image, and further includes a second display module that displays a perspective corrected view of a portion of the image. Moreover, the processor can include a correlation module that effects the display of a graphical object on the displayed wide angle image to identify the selected portion of the image displayed in the perspective corrected view. The processor can effect the display of the fish-eye image on any suitable display, such as, in a window on a computer screen or on a television monitor. The graphical object can be, for example, in the form of a window or a magnifier glass or any other suitable visual icon, that is overlayed on, or otherwise linked to, a portion of the displayed fish-eye image that corresponds to the perspective-corrected view.
In another aspect, the processor effects the display of the fish-eye image and the graphical object associated therewith on a primary display, and presents the perspective-corrected view of a portion of the fish-eye image designated by the graphical object on the primary display, or alternatively, on a separate secondary display.
In further aspects, the processor provides a perspective-corrected view of a portion of a fish-eye image by transforming that portion according to a selected magnification and an angle for viewing a section of a hemisphere corresponding to that image portion from a vantage point offset from the center of the hemisphere by a defined distance.
For example, the processor can effect the correction of a portion of a fish-eye image by mapping a point (u,v) on an undistorted image plane representing a perspective-corrected portion of a distorted image to a point (x,y) on an image plane representing the distorted image by utilizing the following mathematical formulas according to the teachings of the invention:
x=R(xcex20/(PI/2))cos(xcex40)
y=R(xcex20/(PI/2))sin(xcex40)
t=[Dd+sqrt(D2d2xe2x88x92(u2+v2+d2)(D2xe2x88x921))]/(u2+v2+d2)
xcex20=arctan(xe2x88x92D cos(xcex2)+d t cos(xcex2)xe2x88x92v t sin(xcex2), 1)
xcex40=arctan(xe2x88x92D sin(xcex2)+d t sin(xcex2)+vt cos(xcex2), ut)+d
where xcex2 and xcex4 are the zenith and azimuthal angles corresponding to the center of the undistorted image, xcex20 and xcex40 are the zenith and azimuthal angles corresponding to a pixel (u,v) in the undistorted image, d is the magnification factor, D is a distance of a viewing point from the center of hemisphere which correlates with the level of undistortion, and R is the radius of the fisheye image. A more detailed explanation and geometrical definition of these variables will be provided below.
In related aspects, a device of the invention as described above, further includes a user interface module coupled to the processor that allows associating the graphical object with a portion of the displayed fish-eye image, for example, by moving the graphical object to overlie that portion, in order to select that portion of the fish-eye image to be corrected for perspective distortions and to be presented, at a selected magnification, on the same or a separate display for further viewing.
In other aspects, the invention allows selecting a portion of a fish-eye image to be corrected for perspective distortions based on a pre-defined set of rules. For example, in a device of the invention as described above, the processor can be programmed, or can have access to instructions stored in a buffer, to automatically select a portion of an acquired fish-eye image for perspective correction and further viewing. Any instructions suitable for a particular application can be utilized in a device of the invention. For example, the processor may select a rectangular or a circular portion of the fish-eye image centered at a defined region of interest for perspective correction and presentation. Alternatively, the processor can periodically choose a different portion of the fish-eye image, e.g., randomly or based on a pre-defined algorithm, for viewing.
In another aspect, the processor effects the image-capturing device to acquire periodically a fish-eye image of a scene, and compares two or more images, e.g., two successive images, to detect motion, if any, of one or more objects in the field of view. The processor further effects the display of perspective-corrected views of one or more portions of the fish-eye image containing the moving objects, for example, on a secondary display area.
The following embodiments, described with reference to the drawings identified below, provide further understanding of the invention.